Javascript callback function with parameter

Question

The call:

Query.GetDepartments(AcademicYears, function (result) {
 console.log(result)
 })

The function:

exports.GetDepartments = function (callback, AcademicYears) {
 CountAcademicYears = Object.keys(AcademicYears).length;
 switch (CountAcademicYears) {
 case 1:
 AcademicYear1 = AcademicYears[0].Year;
 AcademicYear1 = String(AcademicYear1);
 query = "SELECT [p_departement], [depcode], [departement], [schooljaar] FROM [SA_Departement] WHERE schooljaar='" + AcademicYear1 + "'";
 console.log(query);
 (async function () {
 try {
 let result = await globalConnectionInfordat.request()
 .query(query);
 callback(result.recordset);
 } catch (err) {
 console.log(err);
 }
 })();
 break;
 ..........
 }
}

This gives me this error:

'Incorrect syntax near the keyword \'function\'.',

For some reason, the string isn't read out alright(I think)? Any ideas?

I just need to know how to pass an argument to the function?

EDIT

I had to move the words around for some reason: function (Academicyears, callback) is working.

Thanks for the help!

• Tim Vermaelen: The callback here IS function(result){/*do stuff with result*/} and not inside your callback referring to callback as that's private function from your other method ExecuteSql .
• Kaddath: it works this way: you pass a function as a second parameter, you don't choose when it is called or which argument is passed to it. Your function will be store in a callback local var (this is how exports.ExecuteSql controls when it is executed and what to feed in). In your function, you can use result as you like, but callback is undefined here
• Milan_w: But callback is defined in that function, because that function is also called with a callback?
• Kaddath: not at all, the function you pass as parameter will be the value of callback. "callback" is not a javascript keyword, it is just a variable (a parameter for GetDepartements actually). It could have been named "c" or "dog" just the same, and called with "c(result.recordset)" or "dog(result.recordset)". And this parameter is of course only available for this function GetDepartements. In the new version of the question, you have switched callback and AcademicYears between the definition and the call, so it won't work
• Milan_w: Yeah I'm getting the callback idea a lot better now! But the problem was (I think) that I did an callback 'inception' if you understand what I mean? I changed the code now so that there is no inception anymore and now it works perfectly! thanks!

Answer 1

callback is a local variable. It only exists inside function (query, callback) { /* ... */ }.

You can't use it from outside that function (i.e. in the anonymous function you pass to ExecuteSql).

You would need to create another reference to that function and then use that name:

this.ExecuteSql("SELECT ...", function a_named_function (result) {
 a_named_function(result);
 });

... but recursively calling that function makes no sense.

• Milan_w: That still gives an error. The error comes from the function itself?
• Quentin: @Milan_w — What error? It should now throw an error like "Call stack exceeded" because you are unconditionally calling the function recursively which, as I said in the answer, makes no sense.
• Milan_w: I changed the code. I don't think a callback within a callback will ever work. Can you look at the updated code? This gives me a new error and I don't understand why?
• Quentin: @Milan_w — If you're going to ask a new question about a new error message with new code ... then ask a new question

Answer 2

As per definition of "ExecuteSql", it accepts 2 param. 1. string 2. function.

So when you are calling that module.

it should be:

 this.ExecuteSql("your string", function (result) {
 console.log(result);
 });

Hope this help you.

• Milan_w: This doesn't change the error, the error is not about that callback but about the callback in the function itself.
• surekha shelake: if i understand it correctly. than it should be like this.ExecuteSql("your string", function (result) { anathor_callback(result); }); function anathor_callback(data){ console.log(data); }
• Milan_w: Yeah I'm changing my code a bit so that there is no 'inception'. Please take a look at the updated question